Injection molding apparatus for forming products from molten thermoplastic materials and the like are well known. Contemporary injection molding apparatus generally comprise a two-section mold wherein one of the mold sections is stationary and has an opening for receiving the molten thermoplastic material into a mold cavity defined by the two mold sections in the shape of the product to be formed thereby. The other mold section is movable between an open position away from the stationary mold section and a closed position wherein the two mold sections are in abutted engagement to define the mold cavity.
When molten thermoplastic material is injected under high pressure into the mold cavity, a product is thus formed which conforms in shape to the mold cavity. Upon cooling, the formed product is removed from the mold. Movement of the movable mold section away from the stationary mold section to the open position typically results in the actuation of an ejector which causes the product to be ejected from the mold.
It is also known to utilize a plurality of stations wherein separate injection molding apparatus are utilized to sequentially form separate portions of more complex products, typically utilizing different thermoplastic materials and/or different colors. The product is moved from one station to another to form subsequent portions thereof. A robot arm is typically required to transfer the product from station to station.
Conventional injection molding machines typically utilize a linear action wherein the movable mold section travels in a reciprocating, typically horizontal, linear motion toward and away from the stationary mold section. However, it is also known to utilize a rotary table wherein a plurality of movable molds rotate between stations, one of the stations being an injection station and thus having a port for injecting molten plastic into the mold positioned at that station.
Examples of such rotary injection molding apparatus are provided in U.S. Pat. No. 3,407,443, issued on Oct. 29, 1968, to Beebee et al.; U.S. Pat. No. 3,806,296, issued on Apr. 23, 1974, to Aoki; U.S. Pat. No. 4,424,015, issued on Jan. 3, 1984, to Black et al.; and U.S. Pat. No. 4,613,475, issued on Sep. 23, 1986, to Hettinga. Each of these prior art devices utilize a rotary table having a plurality of molds attached thereto, thus defining a plurality of stations which sequentially engage an injection unit to effect injection molding. Thus, only a single station is being used in the injection molding process at a given time.
Additionally, these prior art devices are generally constrained to be used with stations having identical clamping pressures, strokes, and thermoplastic materials. However, such operation places severe limitations upon the operational capabilities of the rotary injection molding apparatus. By restricting injection molding to a single station at a time, output is considerably restricted. Likewise, by generally requiring that the clamping pressure, stroke, and thermoplastic material utilized be the same for each station, flexibility is considerably reduced.
As such, in view of the shortcomings of the prior art, it is desirable to provide a rotary injection molding device wherein each station may be simultaneously utilized in an injection molding process and wherein the clamping pressure, stroke, and thermoplastic material are variable from station to station as desired. It is further desirable to retain the mold oriented position of the finished ejected product.